D. Edidin, B. Hassett, A. Kresch, A. Vistoli
A natural question is to determine which algebraic stacks are qoutient stacks. In this paper we give some partial answers and relate it to the old question of whether, for a scheme X, the natural map from the Brauer goup (equivalence classes of Azumaya algebras) to the cohomological Brauer group (the torsion subgroup of $H^2(X,{\mathbb G}_m)$ is surjective.
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Unramified Brauer group of quotient spaces by finite groups
本文提出了一个通用算法，用于计算有理簇在有限群作用下的商空间的无分歧布劳尔群。
We show that a quotient of a non-trivial Severi-Brauer surface $S$ over arbitrary field $\Bbbk$ of characteristic $0$ by a finite group $G \subset \operatorname{Aut}(S)$ is $\Bbbk$-rational, if and only if $|G|$ is divisible by $3$. Otherwise, the quotient is birationally equivalent to $S$.
In this paper we consider the Brauer groups of algebraic stacks and GIT quotients: the only algebraic stacks we consider in this paper are quotient stacks [X/G], where X is a smooth scheme of finite type over a field k, and G is a linear algebraic group over k and acting on X, as well as various moduli stacks of principal G-bundles on a smooth projective curve X, associated to a reductive group G. We also consider the Brauer groups of the corresponding coarse moduli spaces, which most often identify with the corresponding GIT-quotients. One conclusion that we seem to draw then is that the Brau…
The cohomological Brauer group of weighted projective spaces and stacks
该研究完成了加权射影空间及其栈的扭结构的上同调Brauer群计算，为代数几何相关研究提供了基础结果。
We reinterpret the residue map for the Brauer group of a smooth variety using a root stack construction and Weil restriction for algebraic stacks, and apply the result to find a geometric representative of for the residue of a Brauer class associated to a conic bundle, or more generally a Brauer-Severi bundle.
This paper proves a result on the existence of finite flat scheme covers of Deligne-Mumford stacks. This result is used to prove that a large class of smooth Deligne-Mumford stacks with affine moduli space are quotient stacks, and in the case of quasi-projective moduli space, to reduce the question to one concerning Brauer groups of schemes.
Descent and Brauer-Manin Obstructions on Deligne-Mumford Stacks
该研究在具有拟射粗模空间的有限型光滑分离德利涅-芒福德堆叠上，证明下降障碍包含于布饶尔-马林障碍，且下降障碍与 étale 布饶尔-马林障碍、迭代下降障碍一致，布饶尔-马林障碍也与迭代布饶尔-马林障碍一致。
Brauer group of moduli stacks of parabolic principal bundles over a curve
本文研究了抛物主丛模堆的 Brauer 群，证明其与粗模堆的光滑部分的 Brauer 群相同，并显示了 quasi-抛物主丛的 Brauer 群为零。
Brauer groups of tame stacky curves and their $μ_r$-gerbes
本文研究任意奇异驯顺堆叠曲线上 $μ_r$-gerbe 的 Brauer 群，通过正合序列刻画其短正合与分裂条件，并在光滑底曲线情形给出精确计算公式。
Cohomological invariants and Brauer groups of algebraic stacks in positive characteristic
引入特征p下代数栈的带模p^r系数上同调不变量理论，并据此完成了任意域上椭圆曲线栈的Brauer群与上同调不变量的计算。
Vanishing of Brauer groups of moduli stacks of stable curves
本文证明了亏格$g\geq 2$的稳定曲线模栈的上同调Brauer群消失，并在特定范围内推广至带标记点版本，同时讨论了Deligne-Mumford栈的有限性结果。
We prove that every element of order 2 in the Brauer group of a complex Kummer surface X descends to an Enriques quotient of X. In 'generic' cases this gives a bijection between the set Enr(X) of Enriques quotients of X up to isomorphism and the set of Brauer classes of X of order 2. For some K3 surfaces of Picard rank 20 we prove that the fibres of the map from Enr(X) to Br(X)[2] above the non-zero points have the same order.
Brauer group of moduli stack of stable parabolic $\textnormal{PGL}(r)$-bundles over a curve
本文研究曲线上稳定抛物型 PGL(r)-丛模叠的 Brauer 群，证明其与粗模空间光滑轨迹的 Brauer 群一致，并在一般拟抛物类型与权重条件下完成计算。
We compute the Brauer group of the moduli stack of stable PGL(r)-bundles on a curve $X$ over an algebraically closed field of characteristic zero. We also show that the Brauer group of such a moduli stack coincides with the Brauer group of the smooth locus of the corresponding coarse moduli space of stable PGL(r)-bundles on $X$.
Brauer group of moduli stack of parabolic $\textnormal{PSp}(r,\mathbb{C})$--bundles over a curve
本文证明了亏格至少为3的曲线上全旗抛物PSp(r,C)丛的模堆的Brauer群等于其粗模空间光滑轨迹的Brauer群，并在特定条件下计算了后者，同时处理了部分旗情形。
Let $X$ be a smooth projective surface over an algebraically closed field $k$ such that $char(k) \neq 2$. Let $X^{[d]}$ denote the punctual Hilbert scheme of zero dimensional quotients of degree $d$ and $X^{(d)}$ denote the symmetric product of $X$. For $\ell \neq 2$, we give a formula for the $\ell$-primary part of the Brauer group of $X^{[2]}$. We show that the Hilbert to Chow morphism induces an isomorphism of cohomological Brauer groups for $d=2$ and a similar result for $d \geq 3$. Let $Q(r,d)$ denote the punctual Quot-scheme parametrising zero dimensional quotients of $\mathcal{O}_X^{ \o…
Let k be a field, G a finite group embedded in the k-group SL(n). For k an algebraically closed field, Bogomolov gave a formula for the unramified Brauer group of the quotient SL(n)/G. We develop his method over any characteristic zero field. This purely algebraic method enables us to recover and generalize results of Harari and of Demarche over number fields, such as the triviality of the unramified Brauer group for k=Q and G of odd order. --- Soient k un corps et G un groupe fini plongé dans le k-groupe SL(n).Pour k algébriquement clos, Bogomolov a donné une formule pour le groupe de Brauer …
$\mathbb{A}^1$-connected stacky curves and the Brauer group of moduli of elliptic curves
本文提出商叠动机连通分支 Nisnevich 层的计算公式，据此分类 $\mathbb{A}^1$-连通叠曲线并证明椭圆曲线模叠的 $\mathbb{A}^1$-连通性，同时建立光滑代数叠同伦纯性并恢复 Picard 群计算。
Malle's conjecture and Brauer groups of stacks
本文提出Malle猜想领头常数的栈版本猜想，并引入代数栈的非分歧Brauer群新概念，为研究数域判别式分布提供新框架。
The Brauer groups of moduli of genus three curves, abelian threefolds and plane curves
本文通过计算低阶上同调不变量，确定了特征不为2的域上亏格3曲线模栈、特定条件下平面曲线模栈及3维主极化阿贝尔簇模栈的Brauer群的$\ell$-准原挠。
The Brauer-Manin obstruction on algebraic stacks
本文研究代数堆上的Brauer-Manin集和配对，扩展了Colliot-Thélène和Sansuc的降理论，证明了局部由变分线性群商的堆的Brauer群的 torsion 性，并展示了Brauer-Manin障碍与其它上同调障碍的一致性。
The étale Brauer-Manin obstruction for classifying stacks
本文研究了分类堆栈BG的强逼近问题，证明了étale Brauer-Manin障碍是强逼近的主要障碍。
We study the question of whether the Brauer group is isomorphic to the cohomological one in spectral algebraic geometry. For this, we prove the compact generation of the derived category of twisted sheaves for quasi-compact spectral algebraic stacks with quasi-affine diagonal, which admit a quasi-finite presentation; in particular, we obtain the compact generation of the unbounded derived category of quasi-coherent sheaves and the existence of compact perfect complexes with prescribed support for such stacks. We also study the relationship between derived and spectral algebraic stacks, so that…
Let $S$ be a scheme and let $π: \mathcal{G} \to S$ be a $\mathbb{G}_{m,S}$-gerbe corresponding to a torsion class $[\mathcal{G}]$ in the cohomological Brauer group $\mathrm{Br}'(S)$ of $S$. We show that the cohomological Brauer group $\mathrm{Br}'(\mathcal{G})$ of $\mathcal{G}$ is isomorphic to the quotient of $\mathrm{Br}'(S)$ by the subgroup generated by the class $[\mathcal{G}]$. This is analogous to a theorem proved by Gabber for Brauer-Severi schemes.
On Brauer groups of tame stacks
本文通过比较温驯代数栈与其粗模空间的布劳尔群，发展计算栈的布劳尔群的通用工具，并应用于椭圆曲线模栈和代数闭域上的栈曲线。
We define stacks of uniform cyclic covers of Brauer-Severi schemes, proving that they can be realized as quotient stacks of open subsets of representations, and compute the Picard group for the open substacks parametrizing smooth uniform cyclic covers. Moreover, we give an analogous description for stacks parametrizing triple cyclic covers of Brauer-Severi schemes of rank 1, which are not necessarily uniform, and give a presentation of the Picard group for substacks corresponding to smooth triple cyclic covers.
We prove that the Brauer group of TMF is isomorphic to the Brauer group of the derived moduli stack of elliptic curves. Then, we compute the local Brauer group, i.e., the subgroup of the Brauer group of elements trivialized by some étale cover of the moduli stack, up to a finite 2-torsion group.
Let $X$ be a smooth projective curve over the complex numbers. We compute the Brauer group of the moduli stack of Bruhat-Tits group scheme $\mathcal{G}$-torsors on $X$. When $g(X) \geq 3$ we compute the Brauer group of the regularly stable locus of the coarse moduli space of semi-stable $\mathcal{G}$-torsors.
Let S be a complex Enriques surface; it is the quotient of a K3 surface X by a fixed-point-free involution. The Brauer group Br(S) has a unique nonzero element. We describe its pull-back in Br(X), and show that the surfaces S for which it is trivial form a countable union of hypersurfaces in the moduli space of Enriques surfaces.
We prove that the Brauer group of the moduli stack of elliptic curves $\mathscr{M}_{1,1,k}$ over an algebraically closed field $k$ of characteristic $2$ is isomorphic to $\mathbb{Z}/(2)$. We also compute the Brauer group of $\mathscr{M}_{1,1,k}$ where $k$ is a finite field of characteristic $2$.
Let $G$ be a semisimple linear algebraic group over the field $\mathbb C$, and let $C$ be an irreducible smooth complex projective curve of genus at least three. We compute the Brauer group of the smooth locus of the moduli space of semistable principal $G$--bundles over $C$. We also compute the Brauer group of the moduli stack of principal $G$--bundles over $C$.
We compute the Brauer group of the universal moduli stack of vector bundles on (possibly marked) smooth curves of genus at least three over the complex numbers. As consequence, we obtain an explicit description of the Brauer group of the smooth locus of the associated moduli space of semistable vector bundles, when the genus is at least four.
We compute the Brauer group of the moduli stack of elliptic curves over the integers, localizations of the integers, finite fields of odd characteristic, and algebraically closed fields of characteristic not $2$. The methods involved include the use of the parameter space of Legendre curves and the moduli stack of curves with full (naive) level $2$ structure, the study of the descent spectral sequence in étale cohomology and the Leray spectral sequence in fppf cohomology, the computation of the group cohomology of $S_3$ in a certain integral representation, the classification of cubic Galois e…
Groupes de Brauer algébriques modulo les constants d'espaces homogènes et leurs compactifications
本文证明连通线性代数群齐性空间的代数 Brauer 群对常数 Brauer 群的商到 $\mathrm H^1(K,\operatorname{Pic}\bar X)$ 的自然包含未必为同构，并将结论推广到光滑紧化。
The Brauer group of $BG$ and gerbe structures of moduli spaces
本文研究了具有阶$N$自同构的曲线的$μ_N$-gerbe结构，并确定了其Brauer类，关键在于计算$BG$的Brauer群。
We compute the Brauer group of the moduli stack of hyperelliptic curves $\mathcal{H}_g$ over any field of characteristic zero. In positive characteristic, we compute the part of the Brauer group whose order is prime to the characteristic of the base field.
We study how to use a suitably ample locally free sheaf over a proper Deligne-Mumford stack to furnish an embedding of the stack into a geometric invariant theory (GIT) quotient stack constructed from a finite-dimensional linear representation of the general linear group.
Let k be a field, X a smooth, projective k-variety. If X is geometrically rational, there is an injective map from the quotient of Brauer groups Br(X)/Br(k) into the first Galois cohomology group of the lattice given by the geometric Picard group. In this note, where the main attention is on smooth compactifications of homogeneous spaces of algebraic k-tori, we show how under some hypotheses the map is onto, and how one may in some special case exhibit concrete generators in Br(X). This is applied to the analysis of counterexamples to the local-global principle for norms in biquadratic extensi…
Let $\mathcal{X}$ be a tame proper Deligne-Mumford stack of the form $[M/G]$ where $M$ is a scheme and $G$ is an algebraic group. We prove that the stack $\mathcal{K}_{g,n}(\mathcal{X},d)$ of twisted stable maps is a quotient stack and can be embedded into a smooth Deligne-Mumford stack. When $G$ is finite, we give a more precise construction of $\mathcal{K}_{g,n}(\mathcal{X},d)$ using Hilbert schemes and admissible $G$-covers.
Recent results in geometric invariant theory (GIT) for non-reductive linear algebraic group actions allow us to stratify quotient stacks of the form [X/H], where X is a projective scheme and H is a linear algebraic group with internally graded unipotent radical acting linearly on X, in such a way that each stratum [S/H] has a geometric quotient S/H. This leads to stratifications of moduli stacks (for example, sheaves over a projective scheme) such that each stratum has a coarse moduli space.
Combining work of Peyre, Colliot-Thélène and Voisin, we give the first example of a finite group $G$ such that the motivic class of its classifying stack $BG$ in Ekedahl's Grothendieck ring of stacks over $\mathbb{C}$ is non-trivial and $BG$ has trivial unramified Brauer group.
The purpose of this paper is to lay the foundations of a theory of invariants in étale cohomology for smooth Artin stacks. We compute the invariants in the case of the stack of elliptic curves, and we use the theory we developed to get some results regarding Brauer groups of algebraic spaces.
The bigger Brauer group and twisted sheaves
针对带拟仿射对角线的代数栈，采用de Jong和Lieblich的扭层方法，证明每个G_m-gerbe都来自中心可分代数，即Taylor大布劳尔群等于二次G_m系数平展上同调，也为概形研究提供新结论。
Brauer group of moduli of stable parabolic $\text{SL}(r,\mathbb{C})$ and $\text{PGL}(r,\mathbb{C})$-connections and Higgs bundles over a curve
本文研究了稳定抛物SL(C)连接和Higgs包的模空间的Brauer群，并建立了稳定抛物PGL(C)连接模堆与粗模空间光滑部分的Brauer群相等性。
We prove the existence of tilting objects on some global quotient stacks. As a consequence we provide further evidence for a conjecture on the Rouquier dimension of derived categories formulated by Orlov.
We give a formula for the cohomological invariants of a root stack, which we apply to compute the cohomological invariants and the Brauer group of the stack of admissible double coverings.
We suggest to endow Mumford's GIT quotient scheme with a stack structure, by replacing Proj(-) of the invariant ring with its stack theoretic analogue. We analyse the stacks resulting in this way from classically studied invariant rings, and in particular for binary forms of low degree. Our viewpoint is that the stack structure carries interesting geometric information that is intrinsically present in the invariant ring, but lost when passing to its Proj(-).
We obtain an easy sufficient condition for the Brauer group of a diagonal quartic surface D over Q to be algebraic. We also give an upper bound for the order of the quotient of the Brauer group of D by the image of the Brauer group of Q. The proof is based on the isomorphism of the Fermat quartic surface with a Kummer surface due to Masumi Mizukami.
A characterization of ball quotient stacks
该研究刻画了作为球商栈紧化的光滑真Deligne-Mumford栈，证明了球商紧化的边界除子结构，推广了Deng-Cadorel的结果，所用方法结合了非阿贝尔霍奇对应等理论。
For a complex toric variety $X$ the logarithmic absolute value induces a natural retraction of $X$ onto the set of its non-negative points and this retraction can be identified with a quotient of $X(\mathbb{C})$ by its big real torus. We prove an analogous result in the non-Archimedean world: The Kajiwara-Payne tropicalization map is a non-Archimedean analytic stack quotient of $X^{an}$ by its big affinoid torus. Along the way, we provide foundations for a geometric theory of non-Archimedean analytic stacks, particularly focussing on analytic groupoids and their quotients, the process of analy…
In this paper, we generalize a result of Karpenko on the torsion in the second quotient of the gamma filtration for Severi-Brauer varieties to higher degrees. As an application, we provide a nontrivial torsion in higher Chow groups and the topological filtration of the associated generic variety and obtain new upper bounds for the annihilators of the torsion subgroups in the Chow groups of a large class of Severi-Brauer varieties. In particular, using the torsion in higher degrees, we show indecomposability of certain algebras.
Effective morphisms and quotient stacks
本文通过引入作为分离态射推广的有效态射，建立了判别带分离良模空间的光滑代数栈何时为分离 DM 栈被环面商的赋值准则。
We show that near closed points with linearly reductive stabilizer, Artin stacks are formally locally quotient stacks by the stabilizer. We conjecture that the statement holds etale locally and we provide some evidence for this conjecture. In particular, we prove that if the stabilizer of a point is linearly reductive, the stabilizer acts algebraically on a miniversal deformation space generalizing results of Pinkham and Rim.
In this paper, we study Azumaya algebras and Brauer groups in derived algebraic geometry. We establish various fundamental facts about Brauer groups in this setting, and we provide a computational tool, which we use to compute the Brauer group in several examples. In particular, we show that the Brauer group of the sphere spectrum vanishes, and we use this to prove two uniqueness theorems for the stable homotopy category. Our key technical results include the local geometricity, in the sense of Artin n-stacks, of the moduli space of perfect modules over a smooth and proper algebra, the étale l…
Computing the equivariant Brauer group
该研究针对带有限阿贝尔群G正则作用的光滑射影有理簇，借助伽罗瓦上同调留数与固定轨迹几何，实现了二维、三维商叠[X/G]的Brauer群有效计算，并完成所有G-极小del Pezzo曲面对应Brauer群的计算。
Let ${\mathcal P}{\mathcal M}^α_s$ be a moduli space of stable parabolic vector bundles of rank $n \geq 2$ and fixed determinant of degree $d$ over a compact connected Riemann surface $X$ of genus $g(X) \geq 2$. If $g(X) = 2$, then we assume that $n > 2$. Let $m$ denote the greatest common divisor of $d$, $n$ and the dimensions of all the successive quotients of the quasi-parabolic filtrations. We prove that the cohomological Brauer group ${\rm Br}({\mathcal P}{\mathcal M}^α_s)$ is isomorphic to the cyclic group ${\mathbb Z}/ m{\mathbb Z}$. We also show that ${\rm Br}({\mathcal P}{\mathcal M}^…
It is well known that the category of quasi-coherent sheaves on a gerbe banded by a diagonalizable group decomposes according to the characters of the group. We establish the corresponding decomposition of the unbounded derived category of complexes of sheaves with quasi-coherent cohomology. This generalizes earlier work by Lieblich for gerbes over schemes whereas our gerbes may live over arbitrary algebraic stacks. By combining this decomposition with the semi-orthogonal decomposition for a projectivized vector bundle, we deduce a semi-orthogonal decomposition of the derived category of a fam…
We consider certain universal functors on symmetric quotient stacks of Abelian varieties. In dimension two, we discover a family of $\mathbb{P}$-functors which induce new derived autoequivalences of Hilbert schemes of points on Abelian surfaces; a set of braid relations on a holomorphic symplectic sixfold; and a pair of spherical functors on the Hilbert square of an Abelian surface, whose twists are related to the well-known Horja twist. In dimension one, our universal functors are fully faithful, giving rise to a semiorthogonal decomposition for the symmetric quotient stack of an elliptic cur…
The geometric K-theory of quotient stacks
本文将几何K-理论的构造精化至任意excellent基上商叠的有理K-理论，证明其是该叠K-理论内蕴分解的一部分，并建立了便于计算的诸多性质。
The Brauer Group of $\mathscr{Y}_0(2)$
本文通过结合Antieau-Meier和Shin的方法，确定了$\mathscr{Y}_0(2)$的Brauer群。
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